- Fiber tapping
Fiber tapping is a method to extract signal from an
optical fiber without breaking the connection. Tapping of optical fiber allows diverting some of the signal being transmitted in the core of the fiber into another fiber or a detector.Fiber to the home (FTTH) systems use splitters to allow many users to share one backbone fiber connecting to acentral office , cutting the cost of each connection to the home. Test equipment can simply put a bend in the fiber and extract sufficient light to identify a fiber or determine if a signal is present.Similar techniques can be used to surreptitiously tap fiber for surveillance, although this is rarely done since all electronic equipment used in
telecommunications is required to allow access to any phone line for tapping by legal authorization. Tapping the fiber means that all signals from every communications source being routed through the fiber are presented and must be sorted for relevant data, an immense task when thousands of sources of data or voice may be present.According to reports, tapping fiber was used by the US government for surveillance following the
September 11, 2001 attacks and anuclear submarine , the Jimmy Carter, was modified to allow tappingundersea cable s.Fact|date=April 2008How to detect fiber tapping
One way to detect fiber tapping is by noting increased
attenuation added at the point of tapping. There are, however, tappers which allow tapping without significant added attenuation.In either case there should be a change of
scattering pattern in that point in line which, potentially, can be detectable. However once the tapper has been detected it may be too late since a part of the information has been already eavesdropped.See the NCS reference below for a more complete explanation.
Counter-measures
One counter-measure is
encryption of data. [ [http://www.convergedigest.com/bp-me/bp1.asp?ID=365&ctgy= Blueprint: Metro Ethernet ] ] This does not prevent tapping but does make the stolen data unintelligible to the thief.References
*National Communications Systems Technical Information Bulletin 00-7 (2000) " [http://www.ncs.gov/library/tech_bulletins/2000/tib_00-7.pdf All Optical Networks] " (pdf), includes a tutorial on how to tap fiber and detect it.
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